In recent years, under the circumstance that a random-accessible disk-shaped-media or the like has become popular, the decrease of the time required for the fast forward or backward winding of a tape is also required. The probable solution for decreasing the time required for the fast forward or backward winding of the tape is to increase the running velocity of the tape (hereinafter abbreviated as "tape velocity" in some cases).
However, when the tape come to the end thereof running at a high velocity, the tape or the tape transport of an apparatus is damaged. Therefore, the tape velocity has to be reduced to a safe velocity before the end of the tape (hereinafter abbreviated as "tape end" in some cases) so that the tape or the tape transport is not damaged at the tape end. In this case, for obtaining good effect in decreasing the time for the fast forward or backward winding of the tape, high tape velocity has to be kept up to around the end of the tape, and, the tape velocity has to be reduced as quickly as possible to the safe velocity which does not damage the tape or the tape transport at the tape end after a decelerating measure is taken on the tape.
Hereinafter a conventional tape transport device is described on reference to FIG. 5 which shows structure for performing the fast forward or backward winding of a tape in the conventional tape transport device.
In FIG. 5, a first reel 52, on which a tape is wound from one end thereof, is rotated by a motor 51 in such a manner as to rotate at the rotational velocity which is proportional to the rotational velocity of the motor 51. On a second reel 53, the tape is wound from the other end thereof. A present-position-detecting-unit 54 detects the present position of the tape based on a first and a second rotation detecting signals respectively generated by the first reel 52 and the second reel 53 in such a manner as to have respective frequencies which are proportional to the respective rotational velocities of the first reel 52 and the second reel 53. A velocity detecting unit 55 detects the running velocity of the tape based on the rotation detecting signals generated by the first reel 52 and the second reel 53, and a motor-rotation-detecting-signal generated by the motor 51. A decelerating-position-storing-unit 56 stores the deceleration beginning position of the tape, which is used in the occasion of the fast forward or backward winding of the tape. A comparing unit 57 compares the present position with the deceleration beginning position of the tape. A motor control unit 58 instructs the motor 51 to reduce the rotational velocity of the motor 51 when the comparing unit 57 judges that the present position is located at the deceleration beginning position or behind the deceleration beginning position in the running direction of the tape.
The operation of the conventional tape transport having the above structure is described hereinafter. To begin with, the first reel 52, on which a tape is wound from one end thereof, is rotated by the motor 51 in such a manner as to rotate at the rotational velocity which is proportional to the rotational velocity of the motor 51, whereby the second reel 53, on which the tape is wound from the other end thereof, rotates in such a manner that the tape wound on the second reel 53 is wound up by the first reel 52. The present-position-detecting-unit 54 detects the present position of the tape based on the rotation detecting signals generated by the first reel 52 and the second reel 53. The comparing unit 57 compares the present position detected by the present-position-detecting-unit 54 with the deceleration beginning position stored in the decelerating-position-storing-unit 56. When the comparing unit 57 judges that the present position is located at the deceleration beginning position or behind the deceleration beginning position in the running direction of the tape, the motor control unit 58 instructs the motor 51 to reduce the rotational velocity of the motor 51, whereby the rotational velocity of the motor 51 (i.e., the tape velocity) is reduced.
After that, when the velocity detecting unit 55 detects that the tape velocity is reduced to a predetermined safe velocity which does not damage the tape or the tape transport at the tape end, the motor control unit 58 stops the decelerating instruction to the motor 51, whereby the tape comes to the end thereof running at the safe velocity.
The deceleration beginning position stored in the decelerating-position-storing-unit 56 is set at a position computed in such a manner that the tape velocity can be reduced to the safe velocity which does not damage the tape and the tape transport just before the tape end by reducing the tape velocity with a predetermined uniform deceleration.
FIG. 6 shows an ideal relation between the running velocity of a tape and the time required for reducing the tape velocity from v to v' in the conventional tape transport device. That is, FIG. 6 shows that a tape running at a velocity v is uniformly reduced to a velocity v', which is a maximum tape velocity for avoiding damage on the tape or the tape transport at the tape end, with a predetermined uniform deceleration (i.e., uniform negative acceleration) a by beginning the deceleration of the tape from a deceleration beginning position S (S denotes also the remaining area of the tape at the deceleration beginning position).
In this case, the running dimension L of the tape in the duration of reducing the tape velocity from v (i.e., tape velocity at the deceleration beginning position) to v' (i.e., maximum tape velocity for avoiding damage on the tape or the tape transport at the tape end) is expressed by EQU L=(v-v').sup.2 /2a.
Also, when the thickness of the tape is denoted by d, the deceleration beginning position (i.e. the remaining area of the tape at the deceleration beginning position) S for minimizing the time required for reducing the tape velocity from vto v' is expressed by EQU S=L.times.d
Therefore, by storing the deceleration beginning position S, which is expressed by the above relation, in the decelerating-position-storing-unit 56, the time required for winding up the tape from the deceleration beginning position to the end of the tape is minimized.
The comparing unit 57 compares the present position detected by the present-position-detecting-unit 54 with the deceleration beginning position S stored in the decelerating-position-storing-unit 56. When the comparing unit 57 judges that the present position is located at the deceleration beginning position S or behind the deceleration beginning position S in the running direction of the tape, the motor control unit 58 instructs the motor 51 to reduce the rotational velocity of the motor 51.
The following is a description on the case that the thickness of the tape is reduced to d.sub.1 (d.sub.1 &lt;d) for increasing the recording time or decreasing the cost of the tape. FIG. 7 shows the relation between the running velocity of a tape and the time required for reducing the tape velocity from v to v' in the case that the thickness of the tape is decreased from d to d.sub.1. In FIG. 7, v, v', a, L and S denote the same as in FIG. 6, and, L.sub.1 denotes remaining tape length at the position where the tape velocity is reduced to v'. In this case, the deceleration beginning position S is expressed by EQU S=L.times.d=(L+L.sub.1).times.d.sub.1.
Therefore, EQU L.sub.1 =L.times.(d-d.sub.1)/d.sub.1 (20).
As a result, the time required for winding up the tape from the deceleration beginning position to the end of the tape on the tape having the thickness of d.sub.1 is longer by t which is expressed by EQU t=L.sub.1 /v'={(d-d.sub.1)/d.sub.1 }.times.L/v'.
As described in the above, in the conventional tape transport device, when the thickness of the tape is decreased, the time required for winding up the tape from the deceleration beginning position to the end of the tape considerably increases (i.e., the time required for the fast forward or backward winding of the tape considerably increases when the thickness of the tape is decreased).